1. Field of the Invention
This invention relates generally to a pressure compensated flow control valve and more particularly to a pressure compensated flow control valve which is selectively adjustable to limit the constant rate of flow to the fluid motor.
2. Description of the Prior Art
Many hydraulic systems have a pressure compensated flow control valve for maintaining a constant rate of fluid across a directional control valve regardless of the load on the motor. U.S. Pat. No. 4,193,263 dated Mar. 18, 1980 discloses a variation of the pressure compensated flow control valve in that it is independently variable to determine the constant flow rate when the directional control valve is at a wide open operating position. More specifically, that valve includes a separate rotatable throttle valve element downstream of the main flow control spool to alter the pressure drop across the flow control valve. One of the disadvantages of that arrangement is that the additional rotatable throttle valve element is separate from the flow control spool thereby increasing the complexity and cost of the valve mechanism. Moreover, the parts distribution system would necessarily have to maintain an inventory of both parts thereby further adding to the overall cost of the valve mechanism. Finally, the additional valve element creates an additional leakage path which can cause metering differences for the flow control spool due to changes in hydraulic oil temperature.
The present invention is directed to overcoming one or more of the problems as set forth above.